Radiation-sensitive polymers and positive-working recording materials

ABSTRACT

Radiation-sensitive polymers contain, in the polymer main chain, both acid-labile groups and onium salt groups with nonnucleophilic counterions and are suitable for the production of semiconductor structural elements.

This application is a FWC of application Ser. No. 08/027,902, filed onMar. 8, 1993, now abandoned, which is a Division of Ser. No. 07/844,977filed on Mar. 2, 1992, now U.S. Pat. No. 5,260,410, which is a FWC ofSer. No. 07/507,890 filed on Apr. 12, 1990, now abandoned.

The present invention relates to radiation-sensitive polymers whichcontain acid-labile groups and onium salts in the polymer main chainwhich are decomposed by the action of light and subsequent thermaltreatment to give low molecular weight products which can be removedunder reduced pressure or by treatment with alkaline or polar solvents,so that said polymers are suitable for photoresists.

Radiation-sensitive, positive-working polymers are known. Thus, inparticular poly-(alkyl methacrylates) are used as photoresists sincethey suffer a decrease in molecular weight under the action of light andthus have a higher solubility than the high molecular weight, unexposedareas.

Another class comprises poly-(olefin sulfones), which likewise undergodecomposition on irradiation and release sulfur dioxide.

A number of polymer-bonded sulfonium salts, for example ##STR1## whereR, R' and R" are each alkyl, X is halogen and n is >5, have already beendescribed.

Radiation-sensitive polymers which contain sulfonium salt units in thepolymer side chain are also known (cf. H. Tagoshi and T. Endo, J. Polym.Sci., Part C: Polym. Lett., 26 (1988), 77-81); however, these polymersdo not contain any acid-labile groups but contain spiro-ortho-esters,which crosslink under the action of light.

Photosensitive polymers which contain aryl-onium salts, such as iodoniumor sulfonium salts, in the polymer main chain are also known (cf. J. V.Crivello and J. H. W. Lam, J. Polym. Sci., Chem. Ed., 17 (1979),3845-3858 and J. V. Crivello, J. L. Lee and D. A. Conlon, Makromol.Chem., Macromol. Symp. 13/14 (1988), 145-160). These onium salts areincorporated in polyimide chains and undergo cleavage at the onium uniton exposure, so that a reduction of the molecular weight is achieved.Since the quantum yield of the onium salts is <1, the achievablesensitivity is relatively low.

It is an object of the present invention to provide photoresistmaterials which ensure a homogeneous distribution of the photoactivegroups in the resist layer, have high sensitivity and, if required, arecapable of being developed by the dry method, ie. without the use ofsolvents.

We have now found that this object is achieved, surprisingly, by thenovel radiation-sensitive polymers which contain, in the polymer mainchain, both acid-labile, in particular carbonate, groups and onium saltgroups, in particular sulfonium salt groups, with nonnucleophiliccounterions.

The present invention relates to radiation-sensitive polymers whichcontain, in the polymer main chain, both acid-labile groups and oniumsalt groups, in particular sulfonium salt groups, with nonnucleophiliccounterions.

The novel radiation-sensitive polymers preferably contain units of thegeneral formulae (I) and (III) or (II) and (III) ##STR2## where R¹ andR² are identical or different and are each alkylene, for example of 1 to9 carbon atoms, such as --CH₂ --CH₂ -- or --CH₂ --CH₂ --CH₂ --,phenylene, naphthylene or substituted phenylene, eg. ##STR3## R³ isalkyl, for example of 1 to 9 carbon atoms, eg. methyl or ethyl,cyclohexyl, phenyl, naphthyl or substituted phenyl, eg.4-tert-butylphenyl, 4-methylphenyl or 4-methoxyphenyl,

R⁴ is a trivalent aliphatic or aromatic hydrocarbon radical, eg.##STR4## R⁵ and R⁶ are identical or different and are each alkyl orphenyl or R⁵ and R⁶ together form a 5-membered or 6-membered ring, eg.methyl, phenyl, 4-methylphenyl or --CH₂ --CH₂ --CH₂ --CH₂ --,

R⁷ is alkylene, for example of 2 to 10 carbon atoms, phenylene or1,4-phenylenedialkylene, eg. ##STR5## divalent radicals having branches,eg. being preferred, or divalent silicon-containing radicals, eg.##STR6## and X is halogen, eg. I, Br, ClO₄, F--SO₃, CF₃ --SO₃, BF₄, PF₆,AsF₆ or SbF₆.

The novel radiation-sensitive polymers contain in general from 2 to 50,preferably from 5 to 25, mol % of condensed monomer units havingsulfonium salt groups.

They preferably consist of condensed units, at least one of the unitsstated under (I) with at least one of the units stated under (III) or atleast one of the units stated under (II) with at least one of the unitsstated under (III) ##STR7##

The present invention also relates to a positive-working recordingmaterial in which the exposed parts are removed using an alkalinedeveloper or a polar solvent or under reduced pressure,radiation-sensitive polymers according to one of the preceding claimsbeing used.

The present invention furthermore relates to a process for theproduction of semiconductor structural elements, wherein a novelradiation-sensitive polymer is applied to a substrate which contains asemiconductor material, the radiation-sensitive layer is exposed toelectromagnetic radiation in a desired pattern and if necessary heatedto 60°-120° C., the pattern is developed and the production of thesemiconductor structural element is completed in a conventional manner.

Regarding the components of the novel polymer, the following may bestated:

1. Sulfonium salts

If the novel polymers are synthesized by polycondensation reactions, thesulfonium salt units of the general formula (I) can be incorporated inthe polycondensate via the hydroxyl groups. Examples of such sulfoniumsalts are: ##STR8## R⁸ =H, alkyl, halogen or alkoxy (C₁ -C₆) R⁹ =H,alkyl, halogen, or alkoxy (C₁ -C₆).

Although these sulfonium salts are preferred, it is also possible to usemonomer building blocks in which the condensable groups are localized ata phenyl radical. Examples of such suitable sulfonium salts are:##STR9## X⁻ =Br⁻, Cl⁻, ClO₄ ⁻, FSO₃ ⁻, CF₃ SO₃ ⁻, BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻,SbF₆ ⁻.

2. Cocondensation components

For the purposes of the present invention, the groups incorporated inthe copolymer are those which are readily clearable by an acid. Examplesof such groups are ethers, acetals, ortho-esters, carbonates and others.

Preferably produced acid-labile groups are carbonate groups, so thataliphatic or aromatic diols are suitable cocondensation components.Examples of such diols are: ##STR10##

The polycondensation reactions can be carried out by known methods, byeffecting condensation with the aid of carbonic acid derivatives, suchas phosgene, carbonyl-bisimidazole or other suitable derivatives. Inspecific cases, it proves advantageous to react the diol components withcarbonic acid derivatives before the actual condensation reaction togive active ester compounds of the following structure: ##STR11##

A number of hydroxyl-terminated siloxanes of the following structuralformulae are also suitable: ##STR12## n=1-100

The polycondensation reactions can be carried out by known methods forthe synthesis of polycarbonates using phosgene (cf. D. Braun, H.Cherdron and W. Kern, Praktikum der makromolekularen organischen Chemie,page 257), carbonylbisimidazole (cf. H. Staab, Angew. Chem. 74 (1962),407) or active esters, such as 4-nitrophenyl carbonates (cf. J. Frechet,Makromol. Chem., Rapid Comm. 7 (1986), 121-126). The sulfonium saltscontaining hydroxyl functional groups are condensed in appropriateamounts with the corresponding diols or the active ester derivatives ina suitable solvent.

Another possible method of synthesizing the novel radiation-sensitivepolymers is the preparation of a polycondensate which contains sulfuratoms in the main chain and is subsequently reacted with an iodoniumsalt in accordance with the following equation: ##STR13##

For the synthesis of sulfonium salts via iodonium salts, see J.Crivello, Advances in Polymer Science 62, Springer Verlag Heidelberg1984, page 9, and the literature cited therein.

The molecular weights of the novel polymers are in general from 5,000 to200,000, preferably from 10,000 to 80,000 (molecular weight determinedby light scattering).

For further processing and use, the novel polymers are generallydissolved in a suitable solvent, eg. cyclohexanone, ethylene glycolethyl ether acetate or methylpropyleneglycol acetate, applied as a thinfilm of about 1-2 μm to a substrate, for example a silicon wafer, heatedunder controlled conditions, for example at 60°-120° C., exposedimagewise and again heated under controlled conditions at 40°-120° C.The exposed areas can then be removed using an alkaline or polarsolvent. If necessary, the exposed areas which have decomposed into themonomer building blocks can also be removed under reduced pressure, withor without the aid of a short wash process with a polar solvent, so thatcrisp structures are produced.

Suitable developers are alkaline solutions having a pH of greater than11, for example aqueous solutions of alkali metal hydroxides,tetraalkylammonium hydroxides or amines, or polar solvents, for exampleisopropanol.

For example the novel polymers are suitable for exposure in theshort-wave UV range below 300 nm to X-ray radiation and electron beamsand, where suitable monomer building blocks are chosen, ie. those whichabsorb in the relatively long-wave UV range, or when sensitizers, suchas phenothiazine or perylene, are added, also for exposure in the nearUV range above 300 nm.

The novel radiation-sensitive polymers are suitable for the productionof photoresists, in particular for the production of resists formicrolithography, and as circuit board resists. They possess inparticular high sensitivity, high resolution, good stability to etchingand high resistance to plasmas, in particular oxygen plasmas, whensiloxanes are used in the polymer chain, and may be capable of beingdeveloped by the dry method.

The production of semiconductor structural elements using the novelradiation-sensitive polymers is carried out in a conventional manner bythe photolithography technique, as described in, for example, PeterKastner, Halbleitertechnologie, Vogel-Verlag, Wurzburg 1980, pages 75 to117.

In the Examples which follow, parts and percentages are by weight unlessstated otherwise.

EXAMPLE 1 Synthesis of the polymers via iodonium salts

A polycarbonate is prepared similarly to the method in D. Braun, H.Cherdron and W. Kern, Praktikum der makromolekularen organischen Chemie,Huthig-Verlag, page 257, by using the analogous sulfur compoundbis(hydroxyphenyl) sulfide instead of bisphenol A.

2.44 parts of this polycarbonate(polyoxycarbonyloxy-1,4-phenylenethio-1,4-phenylene), 4.7 parts ofdiphenyliodonium hexafluoroarsenate and 0.2 part of copper-(II) acetateare combined in a flask and stirred for 3 hours at 120° C. The reactionmixture is introduced into a beaker and extracted three times withether. 3.0 parts of a radiation-sensitive polymer which containscarbonate (IR: 1730 cm⁻¹) and sulfonium hexafluoroarsenate groups (IR:700 cm⁻¹) are formed.

Elemental analysis: C:48.8 H:3.9 S:6.4 As:12.1 F:18.7 I:<0.5

Investigation of lithography

2.0 parts of this polymer are dissolved in 8.0 parts of cyclohexanoneand the solution is filtered through a teflon filter having a porediameter of 0.2 μm and is applied in a layer thickness of about 1.0 μmto silicon wafers by spin coating, the silicon wafers having beentreated beforehand with hexamethyldisilazane as an adhesion promoter.The coated wafers are heated for 5 minutes at 90° C. on a hotplate. Thewafers are then exposed imagewise to excimer laser light of wavelength248 nm through a chromium-coated quartz mask in a Suss MA56contact/proximity exposure unit by the contact method. Optimum exposuretimes are from 5 to 10 seconds. After exposure, the wafers are heatedfor 1 minute at 90° C. on a hotplate and then developed by immersingthem for 1 minute in an aqueous alkaline solution, eg. Microposit® MF319 (Shipley). Cleanly developed structures having a resolution of 1 μmare obtained.

EXAMPLE 2

The procedure described in Example 1 is followed, except that, insteadof the polycarbonate of pure bis(hydroxyphenyl) sulfide, a polycarbonateof a 1:1 mixture of bisphenol A and bis-(hydroxyphenyl) sulfide is used.The exposure times are from 10 to 20 seconds, the procedure otherwisebeing as in Example 1, and cleanly developed 1 μm structures arelikewise obtained.

EXAMPLE 3

The procedure described in Example 1 is followed, except that thepolycarbonate from Example 2 is reacted with diphenyliodoniumhexafluorophosphate instead of with the arsenate. The photosensitivityof this polymer is substantially lower, and exposure times of about 50seconds are required.

EXAMPLE 4

Phenylbis-(4-hydroxyphenyl)-sulfonium hexafluoroarsenate is synthesizedaccording to Example 2 in German Laid-Open Application DOS 3,721,740 andbis-(nitrophenyl) 1,1,4,4-tetramethyltetramethylenedicarbonate issynthesized by the method in Makromol. Chem., Rapid Comm. 7 (1986), 123,as starting compounds for the polycondensation reaction.

A radiation-sensitive polymer is obtained by condensation of 4.84 partsof phenylbis-(hydroxyphenyl)-sulfonium hexafluoroarsenate with 4.76parts of bis-(4-nitrophenyl)1,1,4,4-tetramethyltetramethylenedicarbonate in the presence of 12 partsof dry potassium carbonate, 1.2 parts of crown ether 18-crown-6 and 40parts of dichloromethane, by refluxing for a reaction time of 72 hours.The yield of pure white polymer is 2.8 parts. The spectroscopic analysisis in agreement with the expected structure.

Molecular weight (light scattering): 57,500 g/mol

The lithographic investigations are carried out as in Example 1.Exposure times of from 0.5 to 1.5 seconds result and cleanly developed 1μm structures are likewise obtained.

EXAMPLE 5

The procedure described in Example 4 is followed, except thatbis-(4-nitrophenyl) 1,4-phenylenediethylidenedicarbonte is used insteadof bis-(4-nitrophenyl) 1,1,4,4-tetramethyltetramethylenedicarbonate. Theyield is 46%. The investigations are carried out as in Example 1. Withan exposure time of 25 seconds, completely developed structures areobtained.

EXAMPLE 6

The procedure described in Example 5 is followed, except thatphenylmethyl-2,5-dihydroxyphenylsulfonium hexafluorophosphate is usedinstead of phenylbis-(hydroxyphenyl)-sulfonium hexafluoroarsenate. Theyield is 23%. The lithographic investigations are carried out as inExample 1, and cleanly developed structures are likewise obtained ifexposure is effected for 10 seconds.

We claim:
 1. A product prepared by imagewise exposing aradiation-sensitive polymer having a molecular weight determined bylight scattering of between 5,000 and 200,000, which polymer containsboth acid-labile groups and onium salt groups with non-nucleophiliccounterions in the polymer main chain to electromagnetic radiation toproduce exposed and unexposed portions of the polymer, and removing theexposed portions by contact with an alkaline developer or contact with apolar solvent or under reduced pressure, wherein the radiation-sensitivepolymer contains in the main chain, as onium salt groups withnon-nucleophilic counter-ions, units of formula (I) ##STR14## where R¹and R² are identical or different and are each alkylene of 1-9 carbons,phenylene, naphthylene or substituted phenylene of the formula ##STR15##or phenylene substituted by methyl or methoxy, R³ is alkyl of 1-9carbons, phenyl, naphthyl or phenyl substituted by methyl, by butyl, orby methoxy, and X is halogen, ClO₄, F--SO₃, CF₃ --SO₃, BF₄, AsF₆ orSbF₆.